Signed up with adCenter last week. Basically the same set of keywords and bids -- I've added a few keywords but not removed any -- and I went from nearly 5,000 impressions the first day to less than 500 yesterday, in a steady decline.
There doesn't really appear to be much competition for the keywords I'm using.
It could just be that you're receiving incomplete reports from recent days. Adcenter is a little slow about giving you complete reports quickly. I've seen this as well when doing a "yesterday" search on my reports. i'll see 10% of the normal number of impressions. After a few days , the traffic is reported fully.
I know.... it's a pain. They'd better get this fixed soon. It should be one of their top priorities in my opinion.